1. Field of the Invention
This invention relates to exercise devices in which operator exerted force rotates an armature to cause an electromagnetically induced reactive force that opposes the rotational force being exerted by the operator.
2. The Prior Art
It is known in the art of exercise devices to translate a force exerted by an operator of the device into a positive torque that rotates an axial member. Various electromagnetically operated means have been used to oppose the force exerted by the operator by opposing rotation of that axial member.
In such prior art devices, the electromagnetically formed opposition is based upon the well-known fact that a voltage will be induced in an electrical conductor moved at right angles through a primary magnetic field, with the magnitude of that voltage being proportioned to the speed of the moving conductor. If the moving conductor is connected to a load to form a closed loop, a speed-proportional current will flow in the closed loop. This current generates a secondary magnetic field around the moving electrical conductor. The direction and polarity of the secondary magnetic field opposes the direction and polarity of the primary magnetic field. The force produced by the secondary magnetic field therefore opposes the force which is responsible for originally moving the electrical conductor. This opposing force becomes a load against the original moving force.
The magnitude of the opposing force so produced has been controlled in prior art exercise devices through variation of the load coupled to the moving conductor. Resistors, zener diodes, switches, transistors, etc, have been used as a variable load to control the magnitude of current induced in the moving conductor loop and thereby control the magnitude of opposing force. Two such prior art devices are disclosed in Forsman (U.S. Pat. No. 4,084,810) and Lulay et al (U.S. Pat. No. 3,705,721).
In Forsman, a person operating the exercise device disclosed therein applies a force to rotate a drive shaft. An asynchronous motor opposes rotation of the drive shaft by the operator with a constant resistance called the braking moment. This motor has a stator with windings connected to an external AC supply and a rotor of ferromagnetic material having a circular circumference. An epicyclic gearing arrangement operatively connects the drive shaft to the rotor. Rotation of the drive shaft by the operator powers the rotor in a direction that induces current in the stator windings opposing the natural rotation of the motor due to the external AC supply. In order to keep this opposition constant and independent of the rotational speed of the rotor, Forsman discloses a control circuit which senses what force is being supplied by the exercise machine operator, and accordingly adjusts the current flowing through the stator windings.
In Lulay et al, an armature of a generator is rotated by a torque physically generated by the operator of an exercise device. The output of the generator is connected to a variable load, for example, a variable resistor device. An electronic regulator circuit is provided to respond to generator output by increasing or decreasing, as required, the magnitude of the resistance connected to the generator rotor in order to maintain a constant generator output and, therefore, a constant work load for the exercise machine operator. However, the electronic devices required in conjunction with the regulator to maintain the constant generator output are complex and require for their operation an electrical power source independent of the generator output, until the operator begins to generate sufficient power from the generator of the exercise device to power these electronic devices.